Final Fantasy VI has the ultimate party based RPG ending, every single member gets some spotlight in the escape from Kefka's tower if you properly recruited them, with a few closing out character arcs like Locke and Celes's love story. The characters as actors in a play, acknowledging your name changes, that final "and you"... no game has ever done as loving a sendoff as FFVI. That there is two amazing ending sequences is what cements it as the GOAT.
For highest peak moment of pure elation, Ico's ending takes the cake by far.
Dragon Age : Origins ending segment if you live through the final battle is also way up there for me, getting to talk to the party members one last time, see what they have planned for the future, getting to decide on a major change within Ferelden, then even though it's just slides in the epilogue it covers so many of your choices and the consequences of them.